Clinical meaning
Normal sleep architecture cycles through NREM stages (N1, N2, N3 slow-wave sleep) and REM sleep in 90-minute cycles. Sleep regulation involves the circadian system (suprachiasmatic nucleus responding to light via melatonin secretion from the pineal gland) and the homeostatic sleep drive (adenosine accumulation during wakefulness). Obstructive sleep apnea (OSA) results from pharyngeal airway collapse during sleep due to anatomic narrowing (obesity, macroglossia, tonsillar hypertrophy) combined with reduced neuromuscular tone. Repetitive apneas cause intermittent hypoxia, hypercapnia, sympathetic surges, and sleep fragmentation, leading to cardiovascular complications (hypertension, atrial fibrillation, stroke, heart failure). Insomnia involves hyperarousal of the hypothalamic-pituitary-adrenal axis and cortical activation. Restless legs syndrome involves dopaminergic dysfunction in the diencephalon and iron deficiency in the substantia nigra.
Diagnosis & workup
Diagnostics & workup: - Polysomnography (PSG): gold standard for OSA diagnosis (AHI >= 5 events/hour with symptoms or >= 15 regardless) - Home sleep apnea testing (HSAT) for moderate-to-high pretest probability without significant comorbidities - Epworth Sleepiness Scale (ESS) for subjective daytime sleepiness (score > 10 abnormal) - STOP-BANG questionnaire for OSA screening (score >= 3 indicates high risk) - Serum ferritin for restless legs syndrome (target > 75 mcg/L for treatment) - Sleep diary and actigraphy for insomnia and circadian rhythm disorders